A molecule of water consists of an oxygen atom in the center, bonded to two hydrogen atoms in a bent shape (like a banana or a boomerang). Because of oxygen’s small size and larger number of protons, it has a very strong ability to attract the electrons of nearby atoms, including the hydrogen that it is bonded to. This leads the oxygen to be partly negatively charged and the hydrogen partly positively charged, so the whole molecule behaves like a tiny magnet (polar). When water molecules are near each other, they arrange themselves so that the oxygens are positioned near hydrogens on other molecules and they strongly stick together.

This intermolecular force is strong enough that it is called “hydrogen bonding”. No electrons are shared or exchanged, like in covalent or ionic bonding, which makes it about 1/20th the strength of a covalent bond. Hydrogen bonding occurs with any molecule that has a hydrogen bonded to an electronegative atom: nitrogen, oxygen, fluorine, chloride, bromine or iodine. However, this force has the strongest effects on the properties of water, with the molecules small size and two hydrogens that can participate in the bonding. Because of the strong hydrogen bonding, water has properties that are different when compared to other liquids: - - Water strongly interacts with other polar molecules that have partial charges, allowing to dissolve many different materials like salts and many organic compounds. This also allows it to stick to polar surfaces like glass and be drawn up thin tubes in capillary action.

- - Water also strongly sticks to itself, giving it high surface tension. This is why water droplets form (rather than spreading out thinly over a surface).

- - Water takes a lot of energy to disrupt this hydrogen bonding, so water has a high heat capacity and absorbs a lot of energy in order to change temperature or evaporate (from liquid to gas).

- - When becoming solid, water molecules arrange themselves in a very specific lattice that is less dense and more rigid than its liquid form. This allows ice to float in water, rather than sink.

These properties are essential for life on Earth, at least as we know it. Much of the Earth is covered in water, which regulates the surface temperature. Since ice floats rather than sinks, these top layers of ice shield lakes, seas and oceans (and all the creatures living in them) from completely freezing during cold weather. All organisms use water to dissolve and move minerals and nutrients around their cells and their bodies. Water also regulates their internal temperature too. Can you think of other ways that water is essential for life?

Water is a weird hybrid that bonds in a fashion that isn't entirely covalent (atoms sharing the electrons) or ionic (the anion, in this case oxygen, hogging all the electrons). What results is that water is a very polar molecule. This has the following consequences:

1. The boiling point of water is high relative to other similar compounds (e.g. hydrogen sulfide). This is why water is liquid at room temperature. Based on its molecular weight, it should be a gas.
2. The crystal structure of solid water (i.e. ice) places the water molecules farther from each-other than they can pack as a liquid. As a result, liquid water is denser than frozen water.
3. Since water is polar but not ionic, it can easily dissolve ionic substances like salts, but can even dissolve covalently-bonded compounds like sugars, and even then has some limited ability to dissolve non polar substances. This makes water an almost universal solvent.

Water molecules have covalent bonds between the O (oxygen) and each of the H's (hydrogens). They are very strong. Each water molecule can hydrogen - bond with 2 other water molecules. Those are weak bonds that let the water molecules move around a lot among other water molecules. This is a very short answer.